Who are the sirens we know about in Borderlands?

At the start of a new trailer for borderlands, Lillith says

'There are 6 sirens in the universe. I used to be one'

I remember a few mentions of sirens, but it's been a while.

So in the Borderlands universe, before the events of BL3, what are the sirens that we know about and what are their wereabouts?

Also she says she used to be one, but as far as I know, being a Siren is not something you really can stop being one. So what happened?

Initially, Lilith is the only known siren. However, there was some fan speculation that Commander Steele was also a siren (later confirmed in the Origins comic books), due to her having similar tattoos as Lilith.

Borderlands 2 introduced Maya and revealed Angel to be a siren. It also included the idea of there being (only) 6 sirens in the universe. Additionally, it seems to link their powers to eridium and the vaults in some way.

The developer trailers for Borderlands 3 go on to reveal two more sirens: Tyreen Calypso and Amara. We may see more within the game, since it involves the many vaults revealed to exist on different worlds at the end of Borderlands 2.

While the canonicity of the comics may be questioned, we are introduced to a few other sirens. However, only one is named, Asha, and one other dies shortly after revealing Lilith's "heritage".

As for Lilith saying "I used to be one" - this may be as answered within the story of Borderlands 3.